1. Field of the Invention
The present invention relates to a wiring structure and a manufacturing method therefor, a semiconductor device including the wiring structure and a wiring board, and more specifically, it relates to a wiring structure serving as a transmission line for transmitting signals and a manufacturing method therefor, a semiconductor device including the wiring structure and a wiring board.
2. Description of the Background Art
Following the recent shrinkage of design rule of semiconductor devices, the frequencies of signals have approached to the gigahertz (GHz) band, partially exceeding 1 GHz. When the frequency of a signal reaches the GHz band, it is difficult to handle a signal wire as a lumped constant circuit generally employed for designing a semiconductor device and hence the signal wire must be handled as a distributed constant circuit. The term “lumped constant circuit” indicates a circuit handling inductors, resistors etc. as those present on some limited positions thereof with definite sizes. The term “distributed constant circuit” indicates a circuit handling inductors, resistors etc. per unit length of a line as those uniformly distributed over the entire line. In this distributed constant circuit, a path transmitting signals is referred to as a transmission line. This transmission line serves as a line transmitting electromagnetic waves.
In general, a wire in a chip of a semiconductor device is handled as a lumped constant circuit due to a small wiring length. Therefore, no transmission line structure is employed in the chip of the semiconductor device. A wiring board mounted with the semiconductor device generally already employs a transmission line due to a large wiring length (refer to Japanese Patent Laying-Open No. 2002-158227, for example).
FIGS. 12 to 15 are sectional views showing exemplary conventional transmission line structures. FIG. 12 shows a stripline structure including a signal wire 102 embedded in an insulator film 103 and shield wires (ground wires) 101 and 104 formed on the lower and upper surfaces of the insulator film 103 respectively. FIG. 13 shows a microstripline structure including a shield wire (ground wire) 111 formed on a surface of an insulator film 113 and a signal wire 112 formed on another surface of the insulator film 113. FIG. 14 shows a stacked pair line structure including a signal wire 121 and a shield wire (ground wire) 122, identical in width and thickness to each other, formed on both surfaces of an insulator film 123 respectively.
FIG. 15 shows a coaxial cable comprising a signal wire 131 and a shield wire (ground wire) 132 formed to enclose the signal wire 131 through an insulator 133.
As hereinabove described, the wiring board for mounting the conventional semiconductor device employs any of the transmission lines shown in FIGS. 12 to 15.
On the other hand, a wire in the chip of the semiconductor device must also be handled as a transmission line when the signal frequency reaches the GHz band. In order to form a transmission line structure having the stripline structure shown in FIG. 12, for example, a patterning step including lithography, etching and resist removal must be carried out three times in total for forming the shield wires 101 and 104 and the signal wire 102. Therefore, the manufacturing process is complicated and the manufacturing cost is increased. Also when the structure shown in FIG. 13 or 14 is formed as the wire in the chip of the semiconductor device, the patterning step including lithography, etching and resist removal must be carried out twice, to disadvantageously complicate the manufacturing process and increase the manufacturing cost.
In each of the transmission line structures shown in FIGS. 12 to 14 employed in the aforementioned wiring board for mounting the semiconductor device, a shielding effect with the shield wire(s) 101 and 104, 111 or 122 is so insufficient that signal transmission is easily externally influenced following increase of the signal frequency. Therefore, it is difficult to sufficiently suppress the so-called crosstalk, i.e., such a phenomenon that a signal of a signal system leaks into a signal of another signal system.